Coaxial connector



- 1966 5...!- SOMERSET COAXIAL CONNECTOR 2 Sheets-Sheet 1 Filed Oct. 1,1964 INVENTOR.

SHERMAN J. SOMERSET BY Wmiwtw) OW l ATTORNFYQ FIG.

Dec. 13, 1966 5, SOMERSET 3,292,136

COAXIAL CONNECTOR Filed Oct. 1, 1 64 2 Sheets-Sheet 2 INVENTOR.

SHERMAN J. SOMERSET BY W 2;

4 M ATTORNEYS United States Patent f 3,292,136 COAXIAL CONNECTOR ShermanJ. Somerset, Melrose, Mass., assignor to Gremar Manufacturing (30.,Inc., Wakefield, Mass, a corporation of Massachusetts Filed Oct. 1,1964, Ser. No. 403,807 2 Claims. (Cl. 339-177) This invention relates toconnectors for joining together two lines of the coaxial type commonlyemployed in the transmission of radio frequencies and more particularlypertains to coaxial connectors that are attached to the lines in amanner which eliminates the need for soldering.

In the transmission of electrical wave energy, coaxial cables or linesare customarily employed for the transmission of frequencies extendingover a large band of the electromagnetic spectrum. The coaxial linesusually employ a metal jacket or metallic braid as the outer conductorand solid or stranded copper wire is commonly employed as the centerconductor. The metal jacket coaxial cable has a tubular metal sheath,usually a copper or aluminum tube, surrounding the center conductorwhich extends along the longitudinal axis of the tubular sheath. Thecenter conductor of a coaxial cable is maintained in its axial positionand is insulated from the outer conductor by a dielectric spacer whichcan take a variety of forms such as glass or plastic beads, a spiral ofplastic material, a foamed plastic, or a solid dielectric filler. Abraided coaxial cable, in contrast to a metal-jacketed cable, employs asleeve of braided wire filaments as the outer conductor and the sleeveis usually protected by a covering insulative coat.

The invention pertains to fittings for coupling coaxial cables togetherso as to provide a mechanically strong joint while maintainingelectrical continuity between the coaxial lines in a manner thatsubstantially reduces impedance discontinuities. Much engineering efforthas been expanded in attempts to produce coaxial connectors havingoptimum electrical continuity and V.S.W.R. (voltage standing wave ratio)characteristics. The coaxial connectors heretofore available have, inthe main, failed to approach even moderately closely the theoreticallyattainable optimum characteristics. This invention provides a coaxialconnector constructed so that the characteristic impedance of thecoaxial lines is maintained substantially unchanged in the connector.

Convention coaxial connectors, to insure good electrical contact, havethe center contact arranged so that the center conductor of the coaxialcable can be soldered to it. To permit the soldering operation to beperformed by the purchaser, conventional coaxial connectors areconstructed so that the center contact can be removed from the shell ofthe connector and, after soldering, be reassembled into the connector.In some conventional coaxial connectors even the outer conductor of thecable is soldered to the shell of the connector.

It is an objective of the invention to provide a coaxial connector thatcan be attached in a simple manner and without soldering to the coaxialline. A connector constructed in accordance with the invention, isattached to the coaxial line simply by baring a length of the linescenter conductor, inserting the prepared end of the line into theconnector, and tightening a nut on the end of the connector.

The invention, both as to its construction and mode of operation, can bebetter understood from the following exposition which is intended to beconsidered in conjunction with the accompanying drawings in which:

FIGS. 1 and 2 depict a coaxial line having its end prepared forattachment to a connector constructed in ac cordance with the invention;

3,292,136 I Patented Dec. 13, 1966 FIG. 3 is an exploded view of a maleconnector embodying the invention;

FIG. 4 is a cross-sectional view through the assembled male connector;

FIG. 5 is an exploded view of the invention embodied as a femaleconnector; and

FIG. 6 depicts, in cross-section, the assembled female connector.

Referring now to FIGS. 1 and 2, a metal-jacketed coaxial cable 1 isshown having its center conductor 2 exposed by the removal of the metaljacket and the solid dielectric filler 3. The end of the cable isdressed to remove any burrs and to insure that the shoulder 4 is aplanar surface that is perpendicular to the center conductor 2. As usedherein and as indicated in FIG. 2, the lower case letter d designatesthe diameter of the center conductor of a coaxial line, whereas theupper case letter D designates the internal diameter of the outerconductor of the coaxial line.

FIG. 3 is an exploded view of the male connector which is depicted inassembled form in FIG. 4. The shell or body of the connector is a hollowmetal cylinder 5 having internal threads 6 at one end which are engaged,in FIG. 4, by the cooperating threads of a nut 7. Nut 7 has a centralbore of a size permitting the .coaxial line 1 to be passed through thenut into the interior of the connector. The central bore of nut 7terminates in a flared portion 8 which acts like an inclined plane inforcing a split ring 9 into the shell 5. Each end of split ring 9 istapered, as at 10 and 11, to provide inclined surfaces which coact withthe flared portion 8 of nut 7 and a similar flared opening 12 in theshell 5 to cause the ring to be compressed when nut 7 is turned into theconnectors body. The ring is split along a helix and is provided withinternal teeth which grip the outer conductor of the coaxial line 1 whenthe ring is compressed. The ring, when not compressed, is sufiicientlyresilient to permit the coaxial line 1 to be easily passed through itinto the body of the connector. Within the body 5 of the connector arecylindrical dielectric members 13 and 14 which are constituted by amaterial whose dielectric constant, preferably, is the same as theconstant of the dielectric material employed in coaxial line 1. Thedielectric members have central bores through which extend a centralcontactor 15 having one end adapted to receive the center conductor 2 ofcoaxial line 1 and the other end reduced in diameter.

Disposed concentrically with contactor 15 is an annular metallic element16 having a barrel in which slots are cut. The slots divide the barrelof the annulus 16 into a plurality of resilient fingers. At one end, theannulus 16 has a flange 17 which abuts a shoulder in the shell 5 of theconnector and the annulus is held in the assembly by spinning over aportion of a body 5 to wedge the flange against the shoulder. A washer18, preferably of a material such as Teflon, surmounts the periphery ofannulus 16 and acts as a seal when the male and female portions of theconnector are joined together.

A knurled hollow cylindrical coupling ring 19 is mounted upon theforward end of shell 5. The coupling ring 19 has internal threads 20which mate with matching threads on the female portion of the countershown in FIG. 6. To permit the coupling ring to rotate while preventingits detachment from the body 5 of the male connector, the coupling ringis locked onto the body by a split retaining ring 21 located within agroove 22 in the body 5 and a registering groove in the coupling ring.

When assembling the metal jacketed coaxial line 2 to the male connectorof FIG. 4, the coaxial line has its center conductor bared :as inFIG. 1. The haired end of the coaxial line is inserted through thecentral opening in nut 7 until the bared center conductor is within thecentral contactor 15 and the shoulder of the coaxial line abutsdielectric member 13. The receiving end of the contactor has resilientfingers which grip the hatred center conductor to insure good electriccontact. The nut 7 is then turned into the body to cause split ring 9 tobe compressed by the action of the inclined surfaces. On beingcompressed, the internal teeth of the split ring grip the metal sheathof the coaxial line so that the line is held tightly within the body ofthe connector. As the nut 7 advances, it urges the split ring furtherinto the body, which in turn insures that the shoulder of the coaxialline is pressed against the dielectric member 13. The body of theconnector is provided with a pair of flats" which can be gripped by atool to prevent the body from turning when nut 7 is tightened. A pair ofO-ring seals 23 and 24, dis-posed in grooves within the nut 7 and withinthe body 5, act, when the coaxial line is insered, to seal the interiorof the connector against the entry of moisture and other foreign matter.The O-ring seal 23 also acts to dampen vibrations transmitted along thecoaxial cable 1 and thus inhibits the vibrational forces tending tocause nut 7 to loosen.

It is evident from FIG. 4, that the dielectric members 13, 14 andcentral contactor 15 are locked within the shell 5 of the connector whenthe flange 17 of annulus 16 is wedged into a fixed position by spinningover a portion of the body 5. Once the connector has been assembled, itsconstruction precludes soldering the center conductor 2 of the coaxialcable to the contact-or. It is essential, therefore, when attaching theconnector to the coaxial cable to insure that good electrical contact isestablished between the central contactor and the cables centerconductor as well as between the metal jacket and the shell of theconnector. To insure good electrical contact between the centerconductor and contactor 15, the contactor is preferably constructed byberyllium copper and its fingers are bent inwardly so that .when thecenter conductor is inserted into the contactor, thefingers are forcedoutwardly and grip the surface of the center conductor. Good electricalcontact with the cables metal jacket is insured by the teeth of splitring 9 which, when the ring is compressed, penetrate through any oxidewhich may have formed upon the surface of the metal jacket and grip thejacket so that the cable is locked into the connector.

The characteristic impedance of a coaxial line is given approximately bythe equation:

where When two identical coaxial lines are connected together, changesin the characteristic impedance at the connector give rise toreflections of the wave energy propagating along the lines, the amountof reflected energy being a function of the mismatch. The voltagestanding wave ratio (VSWR) is, therefore, a measure of the impedancediscontinuity existing at the connector. In the ideal connector, thetransition from one coaxial line to the other would be electricallysmooth, that is, the ideal connector would not introduce any impedancediscontinuities. 7

It can be deduced from the equation for the characteristic impedance ofa coaxial line,

that changes in the diameter of the inner conductor d can be offset bychanging the internal diameter D of the outer conductor to maintain thecharacteristic impedance at a constant value. This deduction is used toadvantage in the connector to prevent an impedance discontinuity wherethe coaxial line 1 is joined to the connector.

In the assemblage shown in FIG. 4, the metallic body 5 and the annulus16 function as extensions of the outer conductor of coaxial line 1whereas'the central contactor 15 acts as an extension of the centerconductor 2. Dielectric members 13 and 14 are preferably of the samematerial employed for the medium in coaxial line 1; other materials,however, may be used where their dielectric constants are substantiallythe same as the constant of the dielectric in the coaxial line.

The dielectric member 13 is reduced in diameter for a length 1 at theend abut-ted by coaxial line 1. The distance 1 is the length of thebared center conductor 2 that is not received within central contactor15. For the distance 1 the internal diameter D of body 5, the dielectricconstant e, and the diameter d of the center conductor are identicalwith those of coaxial line 1. The central contactor, for the length hasa diameter d that is larger than the diameter of center conductor 2. Tomaintain a constant characteristic impedance, the inner diameter D ofbody 5 is increased to compensate for the increased value of d Thecapacitance of a coaxial line is given in micromicrofarads per inch (,uf/ inch) by the equation where C is the capacity per unit length,

e is the dielectric constant of the transmission medium in the line,

D is the internal diameter of the outer conductor,

d is the diameter of the inner conductor.

Where a coaxial line of one size is joined to a coaxial line of adifferent size, a mismatch occurs at the junction though the constant eand the ratio D/d, is the same in both lines, unless compensation ismade for the increase in capacitance due to fringing effects of thesharp corners of the transition. Such a transition occurs where thecoaxial line of length 1 joins the coaxial line of length 1 The gapsbetween the resilient fingers of central contactor 15 serve to decreasethe capacity at that transition and, therefore, are effective inoffsetting the capacity due to fringing effects. It has also been foundhelpful to provide a slight champfer on the inside edge at the tips ofthe contactors fingers to provide additional compensation. Othertechniques, such as shaping the contactorto obtain additional inductanceat the transi tion may be used, if desired, to obtain the requisitecompensation.

The central contactor is provided with a flange 25 that is clampedbetween dielectric members 13 and 14 so that the contactor cannot moveaxially. The gap between dielectric members 13 and 14 causes a change inthe value of the dielectric constant e as that gap is filled with air.To maintain the characteristic impedance unchanged, the diameter d3 ofthe flange is such that it offsets the change in 6 caused by the airdielectric in the gap. It has been determined empirically that thelength l;, of the flange 25 should be made as small as possible as abetter impedance match is obtained when the gap between dielectricmembers 13 and 14 is reduced to a length that is insignificant comparedto a wave length of the highest frequency for which the connector isintended. As the flange 25 holds the central contactor against axialdisplacement, it must provide suflicient mechanical strength to performits function adequately. The flange must not be made so thin that thecentral contactor will be sheared off by axial thrust. Using a centralcontactor of beryllium copper, a flange having a length 1 of .020" hasbeen found to be satisfactory for a connector intended for use in theX-band of frequencies.

The mate to the male connector of FIG. 4 is depicted in FIGS. 5 and 6.The body 30 of the female connector is a hollow metallic cylinder.having external threads 31 at its front which are engaged by the matingthreads of the coupling ring on the male connector when the two unitsare united. The rear part of body 30 has internal threads 32 that areengaged by cooperating threads on a nut 33. The nut 33, split ring 34,O-ring seals 35, 36, and dielectric member 37 are identical in shape,arrangement and function to their matching parts in the male connector.

The central contactor 38 of the female connector is prevented from beingdisplaced axially within the body 30 of the connector because the flange39 of the contactor is locked between dielectric members 37 and 40. As

in the male connector, the flange of the central contactor in the femaleconnector is of such diameter that it maintains the characteristicimpedance at a constant value by compensating for the dielectricmembers. The dielectric members, in turn, are secured within the body 30by a metallic liner 41 that is pressed into or otherwise secured to thefront portion of the connectors body. The liner is a hollow cylinderhaving a frusto-conical inner surface 42 terminating in a centralcylindrical cavity.

The front part of the contactor 38 is similar to its rear portion asboth ends of the contactor are hollow cylinders that have slotted toform resilient fingers. The rear portion of contactor 38 secures thecenter conductor of a coaxial line having its center conductor bared asin FIG. 1.

When the male and female connectors are joined together, the reduceddiameter portion 26 of contactor is secured Within and gripped by thefront part of contactor 38 and the barrel of annulus 16 slides alongfrustoconical surface 42. As the barrel of annulus 16 moves into theliner, the resilient fingers of the barrel are compressed, therebyinsuring good electrical contact between the barrel of annulus 16 andthe liner. Ideally, the front edge of annulus 16 should abut theshoulder within liner 42, when the connectors are tightly lockedtogether, so that the abutting annulus presents the same internaldiameter as the central cylindrical bore of the liner.

In the mated male and female connectors, the contactors 15 and 38 act asthe center conductor of an air filled coaxial line having the lining 41and the annulus 16 as its center conductor. To maintain a constant valuefor the characteristic impedance throughout the connectors, the valuesof d and D are adjusted in relation to s so that Z does not change. Forexample, if the characteristic impedance of the metal-jacketed coaxialline of FIG. 1 is 50 ohms, that 50 ohm characteristic impedance ismaintained throughout the male and female connectors even though thetransmission medium in the connectors changes from a solid dielectric,such as Teflon, to air and back to solid dielectric.

While only a preferred embodiment of the invention has been illustratedand described in this exposition, it should be understood that changeswhich do not depart from the essence of the invention can be made and,indeed are apparent to those skilled in the art of electricalconnectors. It is intended, therefore, that the invention not be limitedto the precise device depicted in the drawings, but rather that thescope of the invention be construed in accordance with the appendedclaims.

What is claimed is:

1. An electrical connector for attachement to a coaxial cable, theconnector comprising:

(1) a cylindrical conductive shell having internal threads at one end,the shell having an internal flared opening intermediate its ends,

(2) an elongate contactor having resilient fingers at one end arrangedto surmount and grasp the center concluctor of the coaxial cable, theelongate contactor being within the shell and extending along the shellslongitudinal axis,

(3) dielectric means insulating the contactor from the shell andsecuring the contactor in its axial position within the shell,

(4) a nut having an externally threaded portion adapted to engage theinternal threads of the shell, the nut having a central aperture forpermitting the coaxial cable to extend therethrough into the interior ofthe shell, the central aperture of the nut terminating in a flaredopening,

(5) a split ring adapted to surround a portion of the coaxial cable, thering being split for its entire length along a spiral path, the splitring being disposable in the shell to extend between the nut and theshells internal flared opening, and the split ring having tapering endportions that are urged against the flared openings in the shell and thenut when the nut is advanced into the shell whereby the entire splitring is compressed.

2. An electrical connector for attachment to a coaxial cable, theconnector comprising:

(1) a cylindrical conductive shell having an internal flared openingintermediate its ends;

(2) an elongate ontractor having resilient fingers at one end arrangedto surmount and grasp the center conductor of the coaxial cable, theelongate contactor being within the shell and extending along the shellslongitudinal axis,

(3) a dielectric member having two concentric cylindrical portions ofdifferent diameters, the cylindrical portion of larger diameter having acentral aperture in which the resilient end portion of the contactor isdisposed, the smaller diameter cylindrical portion having a central borepermitting the center conductor of the coaxial cable to extend into thefingers of the contactor, the two concentric cylindrical portions of thedielectric member being disposed within the shell,

(4) means securing the dielectric member and the contactor in fixedpositions within the shell,

(5) a nut having a central aperture for permitting the coaxial cable toextend therethrough into the interior of the shell, the central apertureof the nut terminating in a flared opening, the nut being mounted at oneend of the shell and having threads cooperating with mating threads onthe shell, and

(6) a ring adapted to surround a portion of the coaxial line, the ringbeing split for its entire length along a helical path, the split ringbeing disposable in the shell between the nut and shells internal flaredopenings and the split ring having tapering end portions that are urgedagainst the flared openings when the nut is advanced whereby the entiresplit ring is compressed.

References Cited by the Examiner UNITED STATES PATENTS 2,813,144 11/1957Valach 339-177 X 2,981,920 4/1961 Jackson 339-177 X 3,022,482 2/ 1962Waterfield et al. 339-177 X 3,054,981 9/1962 Malek et a1 339103 X3,076,169 1/ 1963 Blaisdell 339103 X 3,104,145 9/1963 Somerset 339-403FOREIGN PATENTS 778,781 7/ 1957 Great Britain.

EDWARD C. ALLEN, Primary Examiner.

W. DONALD MILLER, Examiner.

1. AN ELECTRICAL CONNECTOR FOR ATTACHMENT TO A COAXIAL CABLE, THECONNECTOR COMPRISING: (1) A CYLINDRICAL CONDUCTIVE SHELL HAVING INTERNALTHREADS AT ONE END, THE SHELL HAVING AN INTERNAL FLARED OPENINGINTERMEDIATE ITS ENDS, (2) AN ELONGATE CONTACTOR HAVING RESILIENTFINGERS AT ONE END ARRANGED TO SURMOUNT AND GRASP THE CENTER CONDUCTOROF THE COAXIAL CABLE, THE ELONGATE CONTACTOR BEING WITHIN THE SHELL ANDEXTENDING ALONG THE SHELL''S LONGITUDINAL AXIS, (3) DIELECTRIC MEANSINSULATING THE CONTACTOR FROM THE SHELL AND SECURING THE CONTACTOR INITS AXIAL POSITION WITHIN THE SHELL, (4) A NUT HAVING AN EXTERNALLYTHREADED PORTION ADAPTED TO ENGAGE THE INTERNAL THREADS OF THE SHELL,THE NUT HAVING A CENTRAL APERTURE FOR PERMITTING THE COAXIAL CABLE TOEXTEND THERETHROUGH INTO THE INTERIOR OF THE SHELL, THE CENTRAL APERTUREOF THE NUT TERMINATING IN A FLARED OPENING, (5) A SPLIT RING ADAPTED TOSURROUND A PORTION OF THE COAXIAL CABLE, THE RING BEING SPLIT FOR ITSENTIRE LENGTH ALONG A SPIRAL PATH, THE SPLIT RING BEING DISPOSABLE INTHE SHELL TO EXTEND BETWEEN THE NUT AND THE SHELL''S INTERNAL FLAREDOPENING, AND THE SPLIT RING HAVING TAPERING END PORTIONS THAT ARE URGEDAGAINST THE FLARED OPENINGS IN THE SHELL AND THE NUT WHEN THE NUT ISADVANCED INTO THE SHELL WHEREBY THE ENTIRE SPLIT RING IS COMPRESSED.